Protective system for electric valve translating apparatus



1940- E. F. w. ALEXANDERSON 2,186,815

PROTECTIVE SYSTEM FOR ELECTRIC VALVE TRANSLATING APPARATUS Filed April7, 193a Fig.1.

" 9 Inventor":

D Ernst FW Alexanderson,

H is Attorny.

current.

I as.

Patented Jan. 9, 1940 A T I Q PROTECTIVE SYSTEM FOR ELECTRIC VALVETRANSLATING APPARATUS Ernst F. W. Alexanderson, Schenectady, N. Y.,

assignor to General Electric Company, a corpcration of New YorkApplication April 7, 1938, Serial No. 200,813

15 Claims. (01. 175-3 3) g My invention relates to electric valvecircuits and more particularly to protective systems for electric valveapparatus of the type employing ionizable mediums such as gases orvapors.

In the use of electric valve apparatus, particularly electric valvesemploying ionizable mediums, it has been found that it is desirable todelay the application of load to the electric valves for a predeterminedtime to permit the cathode to attain a temperature sufficiently great toemit the required electron current. If the load current, or in otherWords the anode-cathode current, is increased to a value beyond thatcorresponding to the cathode temperature, there will be a tendency topull relatively large portions of the elec-- tron emitting surface awayfrom the cathode, thereby reducing the useful life of he valve. Inaddition, it is important in electric valve circuits to maintain thetemperature of the electric valve 'means within a predetermined range ofvalues so that the life of the electric valve means is not unreasonablyshortened. Heretofore, the prior art arrangements have increased theexcitation of the cathode or the cathode heating element as theanode-cathode current increased in order that the electron emission becommensurate with the load imposed on the electric Valve means. Whereelectric valve means employing ionizable mediums are involved,considerable heating of the cathode or the cathode heating elem nt iscaused due to the anode-cathode This heating, in a general Way, is dueprimarily to the positive ion bombardment caused the conduction of theanode-cathode current.

In view of these factors, I have found that there is a decided need fornewand improved electrical control circuits for electric valve meanswhereby the temperature oi the electric valve means is maintained withinreasonable and safe range of values during operation. 1

It is an object of my invention to provide new improved electric valvecircuits.

It is another object of my invention to pro-- vide new and improvedprotective systems for electric valve translating apparatus. 1

It is a further object of my invention to provide new and improvedprotective systems for electric valve apparatus of the type employingionizable mediums and in which the energization of the cathode heatingelement is varied as the anode-.- cathode current changes.

In. accordance with. oneof the illustrated embodiments of my invention,I provide, a protective system for electric, valve apparatus in which acathode heating element is initially energized by a relativelylargecurrent and in which the cathode heating element is energized bycurrents which decrease in value from no load value of the anode-cathodecurrent. The cathode heating element circuit includes a source ofalternating voltage of substantially fixed phase and magniture and alsoincludes a second source of alternating voltage of fixed phase butdisplaced relative to the voltage of the firstsource. The second source:is' preferably displaced by electrical degrees relative to the voltageof the first source and varies in magnitude in accordance In accordancewith another illustrated embodimerit of my invention, the progressivedecrease in energization of the cathode heating element of an electricvalve means is obtained by employing a saturable inductive reactancewhich is connected in series relation between a source of alternati-ngcurrent and the cathode heating element.

The saturable inductive reactance includes a variable impedance windingwhich controls the resultant voltage impressed across the cathodeheating element, a unidirectional magnetizing Winding, and a thirdWinding which is energized in accordance with the anode-cathode currentof the electric valve means and which controls the resultant impedanceof the variable impedancev winding.-

In accordance with a still further feature of one embodiment of myinvention, I provide a protective system for electric valve apparatushaving an anode, a cathode, a'heating element for the cathode, and acontrol member which controls the current conducted by the electricvalve means. lprovide an excitation circuit for controlling the voltageimpressed on the control member and" which'ccmprises a phase shiftingdevice of the rotary type having a movable element. There is providedrestraining means to prevent operation of the movable element and henceto prevent increase of the anode-cathode current of the electric valvesfor a predetermined time after the energization of the cathode heatingelement, thereby aficrding sufiicienttime for the cathode to attain asufficiently high operating temperature. The restraining means mayinclude a izable medium such as a gas or a vapor.

plurality of electro-responsive relays which control the restrainingmeans so that it may be moved progressively in a direction to increasethe anode-cathode current of the electric valves in direct proportion tothe period of energization of the cathode heating elements and after theexpiration of the initial heating period. The control circuit whichelectrically energizes the plurality of electroresponsive relayscomprises an electric valve of the high vacuum type which comprises afilamentary cathode which is energized simultaneously and concurrentlywith the cathode heating elements of the main electric valves which areto be protected,

For a better understanding of my invention, reference may be had to thefollowing description taken in connection with the accompanying drawingand its scope will be pointed out in the appended claims.

Fig. 1 diagrammatically illustrates an embodiment of my invention asapplied to an electric valve translating system including electric valvemeans of the type employing an ionizable medium; Fig. 2 representscertain operating characteristics thereof, and Fig. 3 diagrammaticallyillustrates a still further embodiment of my invention in whichrestraining means is associated with the excitation circuit of theelectric valves to control the rate at which the anodecathode currentmay be increased immediately after the initial energization period ofthe cathode heating elements.

Referring now to Fig. 1 of the accompanying drawing, my invention isdiagrammatically illustrated as applied to an electric valve translatingcircuit for transmitting power between an alternating current circuit Iand a direct current load circuit 2 which may include an armaturecircuit 4 of a direct current motor 3. Direct current motor 3, ofcourse, may include a field winding 5 which is energized from a directcurrent source 6 through a rheostat or adjustable resistance 1. Electrictranslating apparatus is interposed between the circuits I and 2 andincludes a transformer 8 having primary windings 9 and secondarywindings I0, and also includes electric valve means II, I2 and I3 whichare preferably of the type employing an ion- Each of the electric valvesI II3 includes an anode I4 and a hot or thermionic cathode I5, a cathodeheating element I6, and may include a control member I1. A suitablecircuit interrupting means I8 is interposed between the alternatingcurrent circuit I and the transformer 8 and includes an armature memberI9, a closing coil 2!} and a trip coil 2I.

To energize the cathode heating elements I6 and to control the currentsupplied thereto in accordance with the load transmitted by thetranslating apparatus or to control the current supplied to the heatingelements in accordance with the anode-cathode current of the electricvalve means, I provide a cathode heating circuit 22 which includes asource of alternating voltage 23 which may be obtained from thealternating current circuit I through a transformer 24 and a switch 25.The cathode heating circuit 22 also includes a second source of alterwayof an impedance element such as a resistance 26. To energize theresistance 26 in accordance with the anode-cathode circuit of theelectric valves II--I3, I employ a suitable means such as currenttransformer 21. I interpose between the current transformer 21 and theresistance 26 a suitable phase shifting arrangement such as a rotaryphase shifter 28 which is initially positioned to adjust the phase ofthe second alternating voltage relative to the first. I have found thatsatisfactory control of the energization of the cathode heating elementsI6 is obtained when the second alternating voltage provided across theterminals of resistance 26 is displaced substantially 135 electricaldegrees with respect to the source 23 of alternating voltage.

I provide a timing circuit 29 which is energized simultaneously with theclosure of the switch 25 to effect closure of the circuit breaker I8 apredetermined time after the switch 25 has been closed so that there isafforded ample time for the cathode I5 to attain a safe operatingtemperature. The timing circuit 23 comprises a timing element such as anelectric valve 30 of a high vacuum type having an anode 3| and afilamentary cathode 32. The electric valve 30 is designed so that itscathode temperature-time characteristic establishes the interval of timerequired for the proper preheating of the cathodes I5 of electric valvesII-I3. The filamentary cathode 32 is connected to be energized from thecathode heating circuit 22 through a transformer 33. The controlelectric valve 30 effects energization and operation of a relay 34 whichincludes an actuating coil 35, a pair of stationary contacts 36 and 31and cooperating movable contacts 38 and 39. A capacitance 40 may beconnected across coil 35 so that a substantially constant unidirectionalcurrent is transmitted to the coil 35. Contacts 31 and 39 effectenergization of the closing coil of the circuit breaker I8 from asuitable source of current such as a battery 4|. Contacts 36 and 38effect energization of an actuating coil 43 of a time delay relay 42which is employed to connect the rotary phase shifter 28 to theresistance 26. By employing a time delay relay 42, the resultant voltageimpressed across the terminals of cathode heating element I B is notdecreased until after the ex piration of a predetermined interval oftime to insure sufficient initial heating of the oathodes I5.

The operation of the embodiment of my invention shown in Fig. 1 will beexplained by considering the system during the starting operation whenit is desired to subsequently effect energization of the direct currentcircuit 2 from the alternating current circuit I. Circuit breaker Illand switch are initially in the open circuit positions. Upon the closureof switch 25, the cathode heating circuit 22 will be energized and thevoltage of that circuit will be that provided by the source 23 which inturn is supplied by transformer 24. As soon as the switch 25 is closed arelatively large current is transmitted to the cathode heating elementsI6. Current is also supplied to the timing circuit 29. As soon as thecathode 32 of the control electric valve reaches a temperaturesufiiciently high to pass an appreciable anode-cathode current,actuating coil of relay 34 will be energized, effecting closure ofcontacts 36, 38, and 31, 39. This time interval, of course, ispreestablished so that the cathodes [5 of electric valves II--I3 attaina control the magnitude the current transmitted if fi is energized toconnect the transformer ii to v the alternating current circuit i.Goncurrently with this operation, the operating coil 43 of the time"delay relay s2 is energized and after a predcterm'inc-rd time the relaythis moved to the closed circuit position, connecting the phase shifterit to the resistance 245. Brier to the time of the closure of the relayA'Lthe current transniitted to the cathode heating elements It 'ismaximum.- However, after the. closure of the relay &2, the cathodeheating current varies with the load and progressively/decreases :inmagnitude from a maximum value at'no loadtoa minimum value at full load,therebyreducing the amount of current "required Ito operate the electricvalves l l-i3 under full loadconditions. This may be" accomplishedwithout sacrificing the operating characteristics and without shorteningthe life of the tubes since an appreciable heating of the cathodes l5occurs due'to the anode-cathode currents conducted by the electricvalves. I

A better understanding or the manner in which the cathode heatingcurrent varies inresponseg actuating handle 69 so that the handle fitmay to changes in the anodeazathcde current may be obtained by referenceto the operating character; s shown in Fig. 2 Where the vector OArepresents the voltage of source and the vectors AB, AC, and ADrepresent the voltages appearing across the terminals of resistance 25under various load conditions. Accor ingly, vectors A, OB, OC and 0Drepresent the resultant voltages ini'oressed across the terminals of thecathode heat ng element under corresponding conditions and hencerepresentthe magnitudes of the currents transmitted to thc anode-cathodeelements under these conditions. It will be noted that initially theenergization of the cathode heating elements is maximum, correspondingto vector 0A, and that the energizaticn thereof is decreased as the loadincreases from no load to normal or full load. Furthermore, it will benoted that the energization of the cathode heat ing elements itprogressively increases in the overload region, i. e in the region abovenormal or full load.

In Fig. 3, there is shown a further embodiment of my invention in whicha direct current electric valve means 6Q, 56) and iii, which electriovalve meanest-i is of the type employing an ionizable inedium and whichcoir-n anode 52, a cathode lit, a cathode heating element a control.member or grid I A switch 55 is interposed between the alternaf'gcurrent circuit and the transformer d effects energization oi thecathode heat elements it through a transformer lll. I Tothe'anode-cathode current of the elect. ic'valves it- 5L I employ asaturable inductive reactance Ell comprising avariable impedance winding'unidirectionalmagnetizing winding may he iced with direct current fromany suitable source" such as from a direct current source 62 ductive. 1r

through. a switch 63 which is arranged to be operated simultaneouslywith the switch "I provide an excitation circuit tit for energizing thegrids '55 of electric valves til-5i to control the current conducted bythese electric valves. excitation circuit 8d includes a suite e meansforcontrolling the voltages impressed on grids 55, such as a rotaryphaseshifter 65, ineluding a stationary winding and a relatively movablewinding 32 which controls the phase of the alternating voltagesimpressed on grids 55 relative to the anode-cathode voltages of theelectric valves ill-5i;

biasing potential. I provide a suitable actuating member such as ahandle 852, for moving the winding El relative to the Winding 66tocontrol the phase oithe alternating voltages impressed grids 55 ,As ameans for restraining the movement of the handle '89 for a predeterminedtime after the energization of the cathode heat-' ing elements 5??{1provide a device lii'comprising a plurality of 'detent members "ii andi2 and associated electroresponsive actuating devices l3 and M. Thedetent members H and it may he s.. In; biased to engage an extension"la": of the movement of the actuating member 69 in direct relation tothe period of energization of cathode heating elements lid after theexpiration of an initial preehating period, the electrorespcnsivcdevices .l3and l4 rnay be. t vely energized. That is, deVices'TS and imay be'arranged'so that the detent members H and i2 thereof larc.retarded for different values of current conducted through theactuating'coils thereof. The restraining device "iil includes [a springbiased armature which tends to return the actuating member tothe initialvertical position when reset coil Til is .de'energized. 'Ihis resetaction may be effected by any suitable means and is diagrammaticallyillustrated as comprising a pavvland ratchet mechanism 78 and a slidingconnection id. The armature '16 returns the winding t? to a positionwhich maintainselectric valves td-di non-con- I provide a controlandtiming circuit which effects selective energization of theelectrorespcnsive devices l3 and it and which controls these devices inresponse to the period of energization of the cathode heating elementsControl circuit 89 comprises an electron discharge device ill of thehigh .vacuurn type including filamentary cathode 32 which is connectedbe energized concurrently and simultaneowlv with the energizationofthecathode heating l ments 5% from the alternatingv current circuit thr fu'h transformer .83. The, electron dis-- charge device 3i is designed sothat it ailfords an appreciable' interval of time for the energizai anof the cathodeheating'elernents ii iolf electric valves l95l before :itpermits the movement of theactuating member til.

The operation of the embodiment of any in vention shown-[in Fig. will bevexplained by encrgization of considering the system under startingconditions when it is desired to direct current circuit it from thealternating current circuit 45;, Unciithe closure of switches '56 and63, current is supplied tothc cathode heating elements'54 of electricvalves litiii and e A battery [is may be em ployed to impress on thegrids 5'5 a unidirectional arrangedto be selcc-- tary cathode 82 of thedischarge device Bl. The control circuit 80, which is also a timingcircuit, will delay the transmission of current from the direct currentsource 62 to electroresponsive devices l3 and M until the cathodes 53 ofelectric valves G95| have attained a safe operating value. After theexpiration of a predetermined time interval, current will be transmittedby the electron discharge device 8! to efiect the movement of the detentmember l! associated with the electroresponsive devices 13 out ofengagement with the extension 15 so that the actuating handle 69 may bemoved to the dotted position. By such movement, the phase of thevoltages impressed on the control members 55 is advanced relative to theanode-cathode voltages so that the current conducted by the electricvalves 49-5l is increased by increments from a zero value to apredetermined value corresponding to the movement of the actuatinghandle 69. Subsequently, the current transmitted by the electrondischarge device 6| increases to a still greater value, effectingmovement of the detent member 72 out of engagement with the extension'15 so that the current conducted by electric valves 5l may be stillfurther increased. Of course, to permit this movement of actuatingmember 59, the coil Tl is energized moving the armature Hi to theposition shown. If the source of alternating voltage fails, the armatureill will be moved to the right-hand position, returning the actuatingmember 69 to'the vertical initial position in which electric valves 495lare controlled to conduct substantially no current.

The saturable inductive device 58 controls the resultant voltageimpressed across the primary winding of the transformer 51 in accordancewith the anode-cathode current of electric valves l9-5l The windings Giland BI of the saturable inductive reactance are oppositely disposed andby virtue of this fact the heating element current is maximum when theanode-cathode current of the inductive reactance of winding 58 isminimum. As the anode-cathode current increases, inductive reactance ofthe winding 59 increases to decrease the resultant voltage impressed ontransformer 57. In this manner, at low values of anode-cathode current,a relatively large current is transmitted to the cathode heatingelements and as the anode-cathode current increases. the cathode heatingcurrent is progressively decreased in value.

While I have shown and described my invention as applied to a particu arsystem of connections and as embodying various devices diagrammaticallyshown, it will be obvious to those skilled in the art that changes andmodifications may be made without departing from my invention, and I,therefore, in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination, an alternating current circuit, a load circuit,electric translating apparatus connected between said circuits andcomprising electric valve means having an anode, a cathode and a heatingelement for said cathode, a circuit for energizing the cathode heatingelement comprising a source of alternating current for transmitting arelatively large current to the cathode heating element to increase thetemperature of the cathode to a suitable value for operation, means forenergizing the anode-cathode. circuit of said electric valve means, andtime delay means responsive to the energization of the cathode heatingelement circuit for reducing the value of the current supplied to saidcathode heating element as the current transmitted by said translatingapparatus increases.

2. In combination, a supply circuit, a load circuit, electrictranslating apparatus connected therebetween and comprising an electricvalve means having an anode, a cathode and a heating element for saidcathode, means for supplying a relatively large current to the cathodeheating element for a predetermined interval of time to increase thetemperature of said cathode to place said electric valve means incondition for operation, means for energizing the anode-cathode circuitof. said electric valve means at the expiration of said interval, andmeans responsive to the current transmitted by said translatingapparatus for progresively decreasing the value of the current suppliedto the cathode heating element as the current transmitted by saidtranslating apparatus increases from no load to full load value.

3. In combination, a supply circuit, a load circuit, electrictranslating apparatus connected therebetween and comprising an electricvalve means having an anode, a cathode and a heating element for saidcathode, means for supplying a relatively large current to the cathodeheating element for a predetermined interval of time to increase thetemperature of said cathode to place said electric valve means incondition for operation, means for energizing the anode-cathode circuitof said electric valve means at the expiration of said interval, meansfor energizing the cathode heating element comprising a source ofalternating voltage, and means responsive to the current transmitted bysaid translating apparatus for impressing on said cathode heatingelement a resultant voltage the magnitude of which varies in accordancewith the load transmitted by said translating apparatus.

4. In combination, an alternating current circuit, a load circuit,electric translating apparatus connected between said circuits andcomprising electric valve means having an anode. a cathode and a heatingelement for said cathode, circuit interrupting means for connecting saidtranslating apparatus to said alternating current circuit and includinga closing coil, a circuit for energizing the cathode heating element andcompris ing a source of alternating current, time delay means responsiveto the energization of the oathode heating circuit for initiatingenergization of said closing coil, and means responsive to said timedelay means for introducing into the cathode heating circuit analternating voltage which varies in accordance with the currenttransmitted by said electric translating apparatus to control thecurrent supplied to said cathode heating element.

5. In combination, an electric valve means having an anode, a cathodeand a heating element for said cathode, means for energizing the cathodeheating element comprising a source of alternating voltage, and meansfor impressing on said heating element a resultant voltage which variesin magnitude in accordance with the anode-cathode current of saidelectric valve means comprising a source of alternating voltagedisplaced in phase relative to the voltage of said first mentionedsource and being variable in magnitude in accordance with theanodecathode current of said electric valve means.

6. In combination, an electric valve means havode heating elementcomprising a source oralternating voltage, and means for controlling theresultant voltage impressed on said cathode heating element inaccordance with thecurrent oi the anode-cathode circuit of said electricvalve means and comprising a secondsource of alternating voltagedisplaced substantially 135 electrical degrees with respect to thevoltage of said first mentioned sourceand which varies in magnitude- .inaccordance with the anode-cathode 'currentso thatthe voltage impressedacross said heating element is maximum at no load and minimum at fullload. j

Z;. In combination, an electric valve means having ananoole, a cathodeand a heating elementfor said cathode meanafor energizing the cathodeheating element comprising a. source of alternating voltage, and meansfor controlling the resultant voltage impressed across said cathodeheating element comprising a second source of alternating voltageconnected in series relation with the first mentioned. source and whichvaries in accordance with the anode-cathode current of said electricvalve means and which is displaced substantially 135 electrical degreesrelative to the voltage of said first mentioned source so that theresultant voltage impressed across said cathode heating element ismaximum at no load, minimum at the normal full load current of saidelectric valve means and is progressively increased for anode-cathodecurrents above the full load value.

8. In combination, an alternating current circuit, a load circuit,electric translating apparatus connected between said circuits andincluding an electric valve means having an anode, a cathode and aheating element therefore, switching means iorconnecting saidtranslating apparatus to said alternating current circuit and includinga closing coil, a circuit for energizing said heating element, a sourceof alternating voltage for energizing the heating element circuit, timedelay means for energizing said closing coil a predetermined time afterthe energization of the cathode heating circuit, means responsive to thecurrent consumed by saidtranslating apparatus for introducing into thecathode heating circuit a component of voltage of hired phasedisplacement and variable magnitude relative to the voltage of saidsource and comprising an impedance element connected in series relationWith said source and a phase shifting circuit for controlling the phaseof the voltage appearing across the terminals of 'said impedanceelement, and means responsive to the operation of said time delay meansfor connecting said phase shifting circuit to said impedance element apredetermined time after the operation of said time delay means.

9. In combination, a supply circuit, a load circuit, electrictranslating apparatus connected between said circuits and comprising anelectric valve means having an anode, a cathode,

a heating elementior said cathode and atomtrol member, an excitationcircuit for energizing said control member comprising control means forimpressing thereon a voltage to control the current conducted by saidelectric valve means,

and means responsive to the period of energization of said heatingelement for controlling said control means to limit the rate of increaseof the current conducted by said electric valve means. 1

.10. Inrcombination, an alternating current circuit, a load circuit,electric. translating. apparatus connected-between said circuitsandincluding anelectric valve means having an anode, a cathode,aheating'element'for said cathode anda control; member for controllingthe conductivitythere'oi, an excitationcircuit for energizing saidcontrol member to eftectcontrol of the'magnitude of the-currentconducted by said electric valvemeans and including means forcontrolling the voltage impressed on said control member, andmeansassociated with said last mentioned means to prevent operationthereof for a predetermined time after the energization of saidtranslating apparatus.

11. In combination, an alternating currentcir cuit, a load circuit,electric-translating apparatus connected between said circuits andcomprising an electric valve me'ans'including an anode, a cathode, aheating element for said cathode. and a control member, switching meansfor connecting said translating apparatus to said alternating currentcircuit, an excitation circuit for energizing said control member tocontrol the current conducted by said electric valve means and includinga device for controlling the voltage impressed on said control member,means for operating said device, and means for preventing the operationof said last mentioned means for a predetermined time after theenergization of said translating apparatus by the closure of saidswitching means.

12. In combination, an alternating current supply circuit, a loadcircuit, electric translating apparatus connected between said circuitsand comprising an electric valve means having an anode,

a cathode, a heating element for said cathode and a control member, anexcitation circuit for en ergizing said control member to control themagnitude of the current conducted by said electric valve means andincluding a phase shifting device for controlling. the phase of thevoltage impressed on said control member relative to the anode-cathodevoltage, and means for preventing operation of said phase shiftingdevice for a predetermined interval of time after the energization ofsaid translating apparatus.

13. In combination, an alternating current supply circuit, a loadcircuit, electric translating apparatus connected between said circuitsand comprising an electric valve means having an cathode and a controlmember, an excitation circuit for energizing said control member to control the magnitude of the current conducted by said electric valve meansand including a phase shifting device for controlling the phase of theelectric valve means having an anode, a cathode anode, a cathode, aheating element for said 1 I and a control member for .controlling theconr ductivity thereof, an excitation circuit for energizing saidcontrol member and comprising a phase shifting device of the rotary typefor impressing on said control member an alternating voltage variable inphase with respect to the anode-cathode voltage of said electric valvemeans, means for operating said phase shifting device and being biasedto a position to maintain said electric valve means substantiallynonconductive, means for preventing operation of said phase shiftingdevice comprising an electroresponsive relay, and a control circuitcomprising an electronic discharge device having an anode and a cathodewhich is energized from said alternating current circuit concurrentlywith said translating apparatus to control the energization of saidelectroresponsive relay.

15. In combination, an alternating current circuit, a load circuit,electric translating apparatus connected between said circuits andincluding an electric valve means having an anode, a cathode and acontrol member, an excitation circuit for energizing said control memberand comprising a phase'shifting device for impressing on said controlmember an alternating voltage variable in phase with respect to theanode-cathode voltage of said electric valve means and having a movablemember, means for biasing said member to a position to maintain saidelectric valve means nonconductive, means for rotating said member, aplurality of detent members arranged to permit progressive movement ofsaid member and comprising actuating coils, and a control circuitconnected to be energized concurrently with said translating apparatusand including an electronic discharge device for selectively energizingsaid actuating coils in accordance with the period of energization ofsaid translating apparatus.

ERNST F. W. ALEXANDERSON.

